Ethylene gas adsorbent, method of controlling ethylene gas concentration and ethylene gas sensor

ABSTRACT

The present invention provides means which can be used for maintaining the freshness of or controlling maturation of plants or perishables such as fruits, vegetables, and flowers and which is safe to the human body. According to the present invention, a method for maintaining the freshness of or conversely controlling the maturation of plants or perishables by controlling the concentration of ethylene gas by use of an ethylene gas adsorbent containing an alcohol extract solution of raw bamboo and a filter having held thereon the alcohol extract solution of raw bamboo. Also, according to the present invention, there is provided an ethylene gas sensor including a quartz crystal microbalance having coated thereon the alcohol extract solution of raw bamboo.

TECHNICAL FIELD

[0001] The present invention relates to an ethylene gas adsorbent usedfor maintaining the freshness of plants and perishables such as fruits,vegetables, and flowers and to a wrapping material and a packagingmaterial used for maintaining the freshness of plants and perishablessuch as fruits, vegetables, and flowers.

[0002] Also, the present invention relates to an ethylene gasconcentration controlling method and apparatus used for maintaining thefreshness of plants and perishables such as fruits, vegetables, andflowers or for controlling maturation thereof.

[0003] Further, the present invention relates to an ethylene gas sensorthat detects ethylene in a gas and to a method and apparatus formeasuring the concentration of ethylene gas in a gas.

BACKGROUND ART

[0004] Fruits and vegetables such as apples and strawberries, or flowerssuch as carnation are usually packaged in a box in the producingdistrict and transported therefrom. However, there has been a problem inthat ethylene gas generated in the inside of, for example, fruits andreleased therefrom due to fermentation during transportation acceleratesfermentation in other individuals or sites, so that the freshness of thetransported fruits is decreased.

[0005] Accordingly, to transport fruits or other produce, in particular,to a distant location, a method must be adopted in which fruits or thelike are harvested in an unripe state and delivered as they are to thehand of consumers while leaving the fruits to ripen during thetransportation, so that it was difficult to ship the fruits in acompletely ripened state and the delivered fruits in many cases tend tobecome poor in sugar degree or taste.

[0006] As means for solving this problem, a method in which potassiumpermanganate having a capability of decomposing ethylene gas is allowedto coexist during transportation or storage of fruits, vegetables, orthe like to decompose and remove ethylene gas released from the fruitsor vegetables has been proposed (JP 54-117060 A) and partly put topractical use. However, potassium permanganate has a problem of safetyin that it is poisonous when it is swallowed or inhaled and itstimulates the mucous membrane or tissues strongly. Also, a method inwhich an adsorbent of the physical adsorption type, such as zeolite oractivated carbon, is compounded in a wrapping material to thereby adsorband remove ethylene gas has been proposed (JP 64-31838 A). However, themethod exhibits no satisfactory effect. Further, a method in whichvegetables are stored in a refrigerator in coexistence with acopper-containing antimicrobial agent has been also proposed (JP11-211342 A). However, no satisfactory effect has been obtained inpractical use. Furthermore, a method in which transportation isperformed together with fruits having function of absorbing ethylenegas, such as banana and kiwi that are unripe, that is, in a green state,to prevent fermentation has been proposed (JP 11-32668 A). However,fermentation also proceeds in the fruits per se that absorb ethylenegas, so that prolonged effects cannot be expected. In addition, thismethod involves the risk of deteriorating the flavor of the fruit by themixing of the scents due to mixing of different kind of fruits.

[0007] Further, JP 2000-210526 A discloses use of essential oilsobtained by steam distillation of various kinds of plants as materialsfor removing hazardous gases and cites Japanese cypress and tea plant asexamples of such plants. However, the essential oils obtained by steamdistillation of these plants have had no fully satisfactory ability ofremoving ethylene gas.

[0008] Furthermore, as described above, it has been known that plantsand perishables such as fruits, vegetables, and flowers generateethylene gas as a result of fermentation and the released ethylene gasmakes their fermentation proceed further. Accordingly, to controlfermentation of fruits, vegetables, flowers and so forth and maintaintheir freshness, it is important to detect ethylene gas in refrigeratorsand transportation chambers and measure its concentration.

[0009] Conventionally, gas sensors are directed to combustible gases,oxygen, humidity, and hazardous gases such as CO and have come to have abig market. Still now, new needs are created one after another andactive researches are being carried out continuously. One recent bigneed is for detection of scent. Detection of scent finds specificapplications in risk management, food management and the like and at thesame time is a part of sensing of sensibilities, which is a new theme ofinformation science.

[0010] A wide variety of scent components to be detected have beenstudied, examples of which include trimethylamine (TMA) anddimethylamine (DMA) that relate to the freshness of fish and shellfish;methylpyrazine, acetone and the like that are contained in consommésoup; ethyl acetate, acetoin and the like that relate to the freshnessof beef; H₂S and NH₃ that are also hazardous gases; fruit oils,methylmercaptan, aliphatic amines and so forth. However, in actuality,substantially no study has been made for the detection of ethylene gas.

[0011] Conventional materials that have been known as materials for usein scent sensors include metal oxide semiconductors and organicmaterials. In sensors with metal oxide semiconductors, in which sinteredcompacts of oxide particles are mainly used, adsorption or reaction ofscent molecules on or with the surface of the semiconductor particleschanges the electrical resistance of the semiconductor, the amount ofwhich change is taken out as a sensor signal. On the other hand, whereorganic materials are used, adsorption of the scent components on theorganic materials changes the mass, absorbance or the like, the amountof which change is physically measured.

[0012] On the other hand, a method of using a quartz crystalmicrobalance as a sensor using an organic material (Quartz CrystalMicrobalance method (QCM method)) has been known (G. Sauerbrey,“Verwendung von Schwingquartzen zur Wägung dünner Schichten und zurMikrowägung”, Zeitshrift für Physik, Vol. 155, pp.206-222, 1959). Inthis method, a quartz crystal microbalance is used as a high-sensitivitygas sensor element since the quartz crystal microbalance can detect aminute change in mass on an electrode of the quartz crystal microbalancedue to, for example, gas adsorption thereon as a change in resonantfrequency due to mass-loading effect. Further, the QCM method can easilyrealize sensors having various characteristics by varying the sensitivefilm to be coated on the electrode. As the film material, polymers andlipids are mainly used. In the case where scents are distinguished withthe sensors, a technique of pattern recognition by multivariate analysisor through a neural network is used for the recognition of outputs froma plurality of sensors coated with different sensitive films.

[0013] As described above, although hazardous gas sensors or scentsensor shave been conventionally developed, no simple and accurateethylene gas sensor has been developed yet which is suitable fordetecting and measuring concentration of ethylene gas in the gas in arefrigerator or transportation chamber in order to control fermentationof fruits, vegetables, and flowers therein to maintain their freshness.

DISCLOSURE OF THE INVENTION

[0014] The present invention has been made to solve the above problemsof the prior art and therefore an object of the present invention is toprovide means that is safe to human body and used for maintaining thefreshness of plants and perishables such as fruits, vegetables, andflowers for along period of time. Further, another object of the presentinvention is to provide means for accelerating or conversely inhibitingmaturation of plants and perishables such as fruits, vegetables, andflowers.

[0015] The inventors of the present invention have made extensivestudies on the above-mentioned problems and as a result they haveanticipated that use of ethylene monooxygenase that can biochemicallymetabolize and decompose ethylene gas in place of a physical adsorbentsuch as zeolite would solve the above-mentioned problems, therebyachieving the present invention. Then, the inventors of the presentinvention have focused attention, in particular, to an alcohol extractsolution of raw bamboo as a substance containing ethylene monooxygenase.

[0016] That is, in the course of their studies on activated carbon(referred to as carbonized bamboo) obtained by roasting raw green bamboo(hereinafter simply referred to as raw bamboo) used for adsorption ofethylene gas, the inventors of the present invention have found that theraw bamboo itself adsorbs ethylene gas and conceived that use ofethylene monooxygenase, which is an ethylene oxidase contained in rawbamboo, and further an alcohol extract solution of raw bamboo wouldenable adsorption of ethylene gas more efficiently, thereby achievingthe present invention.

[0017] In more detail, the present invention relates to an ethylene gasadsorbent characterized by containing ethylene monooxygenase.

[0018] It is preferable that the ethylene gas adsorbent of the presentinvention further contains a coenzyme (NADPH) in addition to ethylenemonooxygenase.

[0019] The present invention further relates to an ethylene gasadsorbent using raw bamboo fiber or bamboo vinegar that containsethylene monooxygenase, in particular an alcohol extract solution of rawbamboo. As bamboo vinegar, in particular an alcohol extract solution ofraw bamboo is preferable.

[0020] Further, it is preferable that the ethylene gas adsorbent of thepresent invention is held on a substrate such as a transparentsheet-form material and that the ethylene gas adsorbent is held on thesubstrate through a gel forming substance having an amino group.

[0021] The present invention further relates to application of such anethylene gas adsorbent to a wrapping material or a packaging materialfor wrapping or packaging plants and perishables such as fruits,vegetables, and flowers.

[0022] In the case where ethylene monooxygenase in the raw bamboo or thelike of the present invention is used for the adsorption of ethylenegas, the present invention has an excellent advantage in that theethylene monooxygenase causes no danger at all and is safe even if itcontacts with foods and the like and introduced into the body of anindividual or if it is eaten together with the foods since onlynonhazardous plant-based materials are utilized.

[0023] Further, the present invention relates to a method forcontrolling the concentration of ethylene gas with a filter thatethylene monooxygenase is supported thereon. As the substance thatcontains ethylene monooxygenase, in particular an alcohol extractsolution of raw bamboo is preferable.

[0024] It is preferred that said filter further contains NADPH as acoenzyme for ethylene monooxygenase.

[0025] Further, the present invention relates to a method forcontrolling a concentration of ethylene gas with a filter on which a rawbamboo fiber or bamboo vinegar solution. As the bamboo vinegar solution,in particular an alcohol extract solution of raw bamboo is preferable.

[0026] In order to control the concentration of ethylene gas, accordingto the present invention, the method for controlling the concentrationof ethylene gas preferably includes measuring an ethylene gasconcentration of an atmosphere by an ethylene gas concentrationmeasuring apparatus; and decreasing the ethylene gas concentration byoperating a fan to have ethylene gas adsorbed onto the filter when theethylene gas concentration is equal to or above a predetermined value orintroducing ethylene gas into the atmosphere when the ethylene gasconcentration is equal to or below a predetermined value.

[0027] The present invention relates to a method for maintainingfreshness or controlling maturation of perishables such as fruits,vegetables, and flowers, by using the above method for controllingethylene gas concentration.

[0028] Further, the present invention relates to an apparatus forcontrolling ethylene gas concentration which includes the filterdescribed above and a fan and also relates to an apparatus formaintaining freshness or controlling maturation of perishables such asfruits, vegetables, and flowers which is characterized by including anethylene gas concentration measuring apparatus, the filter describedabove, and a fan.

[0029] Furthermore, the present invention relates to an ethylene gassensor that detects ethylene gas in a gas as well as a method andapparatus for measuring the concentration of ethylene gas with saidethylene gas sensor.

[0030] That is, the present invention relates to an ethylene gas sensorcharacterized by including a quartz crystal microbalance having heldthereon ethylene monooxygenase, in particular an alcohol extractsolution of raw bamboo.

[0031] It is preferable that the ethylene gas sensor of the presentinvention further contains a coenzyme (NADPH).

[0032] The present invention also relates to an ethylene gas sensorincluding a quartz crystal microbalance having coated thereon bamboovinegar solution containing ethylene monooxygenase.

[0033] Further, the present invention relates to an ethylene gas sensor,in which the quartz crystal microbalance is coated with the bamboovinegar solution through a gel forming substance having an amino group.

[0034] The present invention also relates to a method and apparatus formeasuring a concentration of ethylene gas in a gas by using the ethylenegas sensor described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 is a reference drawing for illustrating the rate ofabsorption of ethylene gas with respect to raw bamboo or carbonizedbamboo.

[0036]FIG. 2 shows change over time of concentration of ethylene gaswith respect to bamboo vinegar solution.

[0037]FIG. 3 is a schematic diagram of an ethylene gas concentrationmeasuring apparatus of the present invention.

[0038]FIG. 4 shows adsorbability of ethylene gas by a bamboo vinegarsolution.

[0039]FIG. 5 shows adsorbability of ethylene gas with respect to anadsorbent holding a bamboo vinegar solution through a gel-formingsubstance.

[0040]FIG. 6 shows results of experiments of removing ethylene generatedfrom an apple by a bamboo vinegar solution obtained by carbonization.

[0041]FIG. 7 shows results of experiments of removing ethylene generatedfrom an apple by a bamboo vinegar solution obtained by extraction.

[0042]FIG. 8 shows a relationship between ethylene gas adsorbability ofa bamboo vinegar solution obtained by extraction and a substrate.

[0043]FIG. 9 shows a change in concentration of ethylene gas in a sealedcase in which an apple was placed according to Example 8.

[0044]FIG. 10 shows an ethylene gas concentration controlling apparatusof Example 10.

[0045]FIG. 11 shows a change in ethylene gas concentration in a storagechamber according to Example 10.

[0046]FIG. 12 shows the amount of ethylene gas adsorption with respectto the ethylene gas concentration, which is measured with the sensor ofthe present invention.

[0047]FIG. 13 shows comparison between the amount of ethylene gasadsorption and the amount of adsorption of other scent gas measured withthe sensor of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0048] Hereinafter, the present invention will be described in detail.

[0049] The mechanism of ethylene metabolism in a plant tissue isdescribed below. In “Mechanism of CH₂CH₂ metabolism in a plant tissue”,[O] indicates ethylene oxidase (ethylene monooxygenase) As describedbelow, there are two active sites for ethylene metabolism in a plantbody. At an active site I, ethylene is oxidized and converted intoethylene oxide, which is further oxidized through ethylene glycol intocarbon dioxide. At an active site II, after conversion into ethyleneglycol, the ethylene glycol is combined with glucose to form ethyleneglycol-glucose combination.

[0050] In the following description, the mechanism of ethylenemetabolism is shown in more detail.

[0051] Ethylene is converted by an ethylene oxidase (ethylenemonooxygenase) into ethylene oxide, which combines with a receptor tocause a biochemical reaction. On this occasion, NADPH is required as acoenzyme. The chemical reaction is carried out by utilizing energyreleased when the coenzyme is oxidized and decomposed. Further, ethyleneoxide is converted into ethylene glycol at another site and metabolizedinto carbon dioxide. The carbon dioxide has an action of increasingethylene monooxygenase activity. Glyoxylation of ethylene glycol is aroute of detoxication of ethylene (cf., Keishi Shimokawa, “Ethylene”,University of Tokyo Press (1988), p. 76 and 80).

[0052] Initially, the inventors of the present invention have carriedout tests of using raw bamboo cut laterally without any modification andactivated carbon obtained by roasting said cut raw bamboo as ethylenegas adsorbents for maintaining the freshness of plants such as fruits,vegetables and flowers. For the purpose, 25 g each of raw bamboo andactivated carbons (carbonized bamboo) obtained by roasting raw bamboo at300° C., 1,000° C. and 2,000° C., respectively, was charged in a sealedvessel filled with ethylene gas of a concentration of 50 ppm and air wascirculated therein with a fan to carry out ethylene gas removal tests.FIG. 1 shows the results of the ethylene gas removal tests. From theresults shown in FIG. 1, it has been recognized that raw bamboo removedethylene gas best. This has led to anticipation that removal of ethylenegas may be related not to physical adsorption by activated carbon but toplant metabolism of bamboo.

[0053] However, because of poor usability provided by use of raw bambooas it is for the adsorption of ethylene gas, studies have been made tosee if there is a substance that is liquid allowing thin film formationand has an ethylene gas removing effect equivalent to that of rawbamboo. As a result, attention has been focused on bamboo vinegarobtained by dry distillation (carbonization) or extraction of rawbamboo.

[0054] In the present invention, bamboo vinegar is meant a liquidobtained from raw bamboo by dry distillation or extraction, morespecifically, a liquid obtained by dry distillation of powdered rawbamboo at a temperature of 100-300° C. with applying a pressure of 3 to5 atm or a liquid obtained by extracting powdered raw bamboo withalcohol, water or an aqueous solution of an enzyme such as cellulase. Inthe present invention, it is most preferable that an alcohol extractsolution obtained by extracting raw bamboo with an alcohol be used as abamboo vinegar solution.

[0055] Next, the inventors of the present invention have tried toperform ethylene gas removal experiments with a bamboo vinegar solutionobtained from raw bamboo. 100 ml of a bamboo vinegar solution obtainedby dry distillation of raw bamboo was diluted with 300 ml of ultrapurewater, and biodegradable resin foam particulates made of cellulose as amain ingredient were immersed therein for 24 hours and thenspontaneously dried for 24 hours to fabricate a filter. As thebiodegradable resin foam particulates were used particulates formed bypulverizing foam of a thumb size so as to have a large specific surfacearea. The fabricated filter was introduced in a sealed vessel filledwith about 50 ppm of ethylene and air was circulated with a fan. Afterthree hours, ethylene gas removal rate was measured. Table 1 shows theresults obtained. TABLE 1 Ethylene gas removal rate InitialConcentration concentration after three hours Bamboo vinegar 55 ppm  0.2ppm solution/foam Foam only 58 ppm 21.0 ppm

[0056] From the results, it can be seen that the foam immersed in thebamboo vinegar solution considerably increased the removal rate ascompared with the foam alone.

[0057] As described above, in a plant body, ethylene is converted intoethylene oxide by an ethylene oxidase (ethylene monooxygenase) andfurther into ethylene glycol and finally metabolized into carbondioxide. From this and the above-mentioned test results obtained by theinventors of the present invention that a radial section of raw bambooor a bamboo vinegar solution exhibits the effect of adsorbing ethylenegas, the inventors of the present invention have presumed thatcatabolism (destructive metabolism) of ethylene with an enzyme containedin raw bamboo or a bamboo vinegar solution may be involved in theability of removing ethylene gas by raw bamboo or a bamboo vinegarsolution.

[0058] On the other hand, the inventors of the present invention haveanalyzed raw bamboo and a bamboo vinegar solution and as a result theyhave confirmed that the raw bamboo or the bamboo vinegar solutioncontained ethylene monooxygenase belonging to ethylene oxidase.

[0059] From the above-mentioned tests and analyses, the inventors of thepresent invention have obtained the knowledge that any material thatcontains ethylene monooxygenase, not limited to raw bamboo or a bamboovinegar solution, is effective for adsorbing ethylene gas.

[0060] Further, based on the following experiments, the inventors of thepresent invention have found that among various kinds of plant extractsolutions, an alcohol extract solution of raw bamboo is particularlysuitable for the adsorption of ethylene gas. That is, the inventors ofthe present invention have carried out ethylene gas removal tests withalcohol solutions of Japanese cypress and of a tea plant and comparedthe results thereof with those of an alcohol solution of raw bamboo.Here, a liquid obtained by extracting 100 g of powder of each plantcharged in a vessel with 70 cc of ethanol was used as an extractsolution. As an adsorbent, used was one obtained by holding each extractsolution on a substrate made of a biodegradable foam through chitosanthat is a gel forming substance having an amino group. Table 2 shows theresults of measurement of ethylene gas concentration after five daysfrom introduction of each adsorbent in a sealed vessel filled with 100ppm of ethylene gas. TABLE 2 Ethylene gas removing ability Initial Afterremoval concentration five days rate Adsorbent (ppm) (ppm) (%) Bambooextract solutions/ 100 40 to 50 50 to 60 chitosan/substrate Japanesecypress/ 100  95 5 chitosan/substrate Tea plant/ 100 100 0chitosan/substrate

[0061] From Table 2, it can be seen that the alcohol extract solution ofraw bamboo exhibits an ability of removing ethylene gas 10 times or morein comparison with those of the alcohol extract solutions of Japanesecypress or tea.

[0062] Next, the inventors of the present invention have compared thealcohol extract solution of raw bamboo with the dry distillate of rawbamboo with respect to their ability of ethylene gas adsorption. FIG. 2shows the results. In FIG. 2, an alcohol extract solution of raw bamboois represented as bamboo extract and a dry distillate of raw bamboo isrepresented as bamboo vinegar. In FIG. 2, the solid lines indicateabilities of ethylene gas removal, with the horizontal axis indicatingnumber of days and the vertical axis indicating ethylene gasconcentration. From the results, it can be seen that the ability ofethylene gas adsorption is more excellent for the alcohol extract of rawbamboo than for the dry distillate of raw bamboo. Note that in FIG. 2,the concentration of ethylene glycol released as a result of adsorptionand oxidation of ethylene gas is also described (broken lines). Also, areleased amount of ethylene glycol is more in the alcohol extractsolution than in the dry distillate.

[0063] In the ethylene gas adsorbent of the present invention, rawbamboo, a bamboo vinegar solution or the like that contains ethylenemonooxygenase is preferably held on a substrate. The substrate may be inany form, such as a film, sheet, granule, or mass. Examples of thematerial used for the substrate include polyethylene, polystyrene, woodpulp, cellulose, polyvinyl chloride, polyvinylidene chloride,cellophane, and cardboard box material. They may be made of foams.

[0064] In particular, when the ethylene gas adsorbent of the presentinvention is used as a wrapping material for plants such as fruits,vegetables and flowers, the substrate is preferably a transparent filmsuch as a polyethylene sheet that can be seen through and morepreferably a cellophane paper in order to arouse willingness topurchase.

[0065] When the ethylene gas adsorbent of the present invention is usedas a packaging material for plants such as fruits, vegetables andflowers, wood pulp or natural cellulose sheets are preferable assubstrates.

[0066] To hold the bamboo vinegar solution on a substrate, the bamboovinegar solution as it is may be applied onto the substrate byimmersion, casting or coating. However, holding the bamboo vinegarsolution on a substrate through a gel forming substance having an aminogroup is preferred since the ethylene gas adsorption rate is increased.

[0067] It is presumed that holding a bamboo vinegar solution on asubstrate through a gel forming substance having an amino group resultsin an increased ethylene gas adsorption rate because an amino group canreact with a carboxyl group of the enzyme protein in the bamboo vinegarsolution to immobilize the enzyme.

[0068] A preferable substance as the gel forming substance having anamino group includes polyallylamine, polyethyleneimine and chitosan.Chitosan has two amino groups in the molecule and in addition isharmless so that it is more preferable. When chitosan is used, it ispreferable that a weak acid harmless to the human body, such as aceticacid or citric acid, be added to chitosan to form a transparent solutionbefore it can be used.

[0069] The bamboo vinegar solution and the gel forming substance may bemixed with each other and held on a substrate or the gel formingsubstance may be held on a substrate and the bamboo vinegar solution maybe laminated on the gel forming substance so as to be held thereon.

[0070] For example, the adsorbent of the present invention can beproduced by using a solution prepared by mixing a bamboo vinegarsolution with an aqueous solution of polyallylamine or an aqueoussolution of chitosan in citric acid and coating or immersing a substratesuch as a cellophane paper with or in the solution. Further, theadsorbent of the present invention can also be produced by coating asubstrate with a solution of polyallylamine or chitosan in citric acid,drying the coating, further coating a bamboo vinegar solution on thecoating, and drying the resulting coating.

[0071] Thus far, the ethylene gas adsorbent of the present invention hasbeen explained as one used for holding the freshness of plants such asfruits, vegetables and flowers but the ethylene gas adsorbent of thepresent invention can be used as a filter for removing ethylene gas aswell.

[0072] In the present invention, a method for controlling ethylene gasconcentration includes decreasing the ethylene gas concentration byhaving ethylene adsorbed on a filter to remove ethylene from theatmosphere or conversely, increasing the ethylene gas concentration byhaving ethylene released from the filter. Ethylene can be eliminatedfrom the atmosphere when it is desired to control the maturation ofperishables such as fruits, vegetables and flowers to maintain thefreshness thereof, and conversely ethylene can be desorbed from thefilter so as to release to the atmosphere when it is desired toaccelerate the maturation.

[0073] In the ethylene gas filter of the present invention, the rawbamboo fiber, bamboo vinegar solution, or the like that containsethylene monooxygenase is held on a filter substrate. The filtersubstrate may be in any form selected from film, sheet, nonwoven fabric,woven fabric, granules, or mass and the material used for the substrateincludes polyethylene, polystyrene, wood pulp, cellulose, polyvinylchloride, polyvinylidene chloride, artificial fibers, animal fibers,plant fibers and glass fibers. These may be foams.

[0074] To hold raw bamboo fibers on a substrate, raw bamboo fibers aremixed into a filter substrate such as a foam, nonwoven fabric, or thelike, or are adhered onto a surface of the filter substrate.

[0075] To hold a bamboo vinegar solution on the filter substrate, thebamboo vinegar solution as it is may be applied onto a substrate byimmersion, casting or coating. However, holding it on a substratethrough a gel forming substance having an amino group is preferred sincethe adsorption rate of ethylene gas is increased.

[0076] In the present invention, when a bamboo vinegar solution is usedin an ethylene gas sensor, the bamboo vinegar solution is held on aquartz crystal microbalance. To hold the bamboo vinegar solution on aquartz crystal microbalance, the bamboo vinegar solution as it is may becast or coated onto the quartz crystal microbalance but, as well as inthe case where the bamboo vinegar solution is used in an absorbent or afilter, it is preferred that the bamboo vinegar solution be held on thesubstrate through a gel forming substance having an amino group sincethe ethylene gas adsorption rate is elevated.

[0077] The bamboo vinegar solution and the gel forming substance may bemixed with each other and held on a quartz crystal microbalance or thegel forming substance may be held on a quartz crystal microbalance andthe bamboo vinegar solution may be laminated on the gel formingsubstance so as to be held thereon.

[0078] For example, the sensor of the present invention can be producedby using a solution prepared by mixing a bamboo vinegar solution with anaqueous solution of polyallylamine or an aqueous solution of chitosan incitric acid and coating or casting a quartz crystal microbalancetherewith. Further, the sensor of the present invention can also beproduced by coating a quartz crystal microbalance with a solution ofpolyallylamine or chitosan in citric acid, drying the coating, furthercoating a bamboo vinegar solution on the coating, and drying theresulting coating.

[0079] Hereinafter, examples of the present invention will be described.However, the present invention should not be considered to be limitedthereto.

EXAMPLE 1

[0080] (Production of a Sensor)

[0081] A bamboo vinegar solution was obtained by charging powder of mosobamboo (Phyllostachys pubescens) in a basket and dry distilling it at300° C. and at 5 atm for 4 hours. 0.2 μl of the bamboo vinegar solutionwas cast on an electrode of a quartz crystal microbalance andspontaneously dried for 24 hours to obtain a sensor.

[0082] (Ethylene Gas Adsorption Test)

[0083] The sample thus obtained was inserted in a sealed vessel in whichthe ethylene gas concentration was kept at a constant level of 150, 300,or 800 ppm, and after 100 seconds the sample was taken out into the air.The measurement was repeated three times.

[0084] (Method of Testing Adsorption Amount)

[0085] The adsorption amount of ethylene gas was measured by use ofquartz crystal microbalance method (QCM method). The QCM method utilizesthe phenomenon that the eigen frequency of a quartz crystal microbalanceis changed due to a change in mass attached to the electrode. When atrace substance is attached onto the electrode of a quartz crystalmicrobalance by gas adsorption or the like, these minute mass change canbe detected as a change in resonant frequency due to a mass loadingeffect.

[0086]FIG. 3 shows a schematic diagram of an apparatus using the QCMmethod.

[0087] Reference numeral 1 designates a quartz crystal microbalancehaving cast thereon with ethylene monooxygenase, 2 designates anoscillation circuit, 3 designates a resonant frequency detector, and 4designates a computer. A change in frequency appearing at 3 as a resultof adsorption of ethylene gas supplied from an ethylene gas source 5 toa sealed vessel 6 onto the quartz crystal microbalance 1 is detected.

[0088] (Results)

[0089]FIG. 4 shows the results. In FIG. 4, (1) shows the case in whichthe ethylene gas concentration was 150 ppm, (2) shows the case in whichthe ethylene gas concentration was 300 ppm, and (3) shows the case inwhich the ethylene gas concentration was 800 ppm. From those results, itcan be seen that in any case in which the ethylene gas concentration was150, 300 or 800 ppm, when the quartz crystal microbalance on which thebamboo vinegar solution was cast was inserted into the sealed vessel,adsorption of ethylene gas was started, while when the quartz crystalmicrobalance was exposed to the atmospheric air, the adsorbed ethylenewas released. From this it was revealed that the quartz crystalmicrobalance having cast thereon with the bamboo vinegar solution couldbe used as an ethylene gas sensor. According to FIGS. 4 (1) to (3), thesaturated adsorption amounts in respective cases are substantially equaland differences are minute.

EXAMPLE 2

[0090] In Example 2, ethylene gas adsorbent and a sensor comprising acomposite film with a gel forming substance having an amino group areshown.

[0091] Before casting a bamboo vinegar solution on a quartz crystalmicrobalance, polyallylamine hydrochloride (PA) was used as a binder andthe bamboo vinegar solution was cast thereon to prepare a composite filmof PAH and the bamboo vinegar solution. First, the quartz crystalmicrobalance was subjected to hydrophilic treatment with KOH and 0.2 μlof a PAH solution was cast thereon and spontaneously dried for 24 hoursto fabricate a thin film. Thereafter, 0.2 μl of the bamboo vinegarsolution was cast and spontaneously dried for 24 hours to prepare acomposite film. Quartz crystal microbalances with the prepared compositefilm, a single film of PAH or a single film of the bamboo vinegarsolution, respectively was put into and out from a sealed vessel ofwhich the ethylene concentration was 200 ppm and responses of adsorptionand desorption were observed. FIG. 5 shows the results. In FIG. 5, thevertical axis indicates ethylene gas adsorption amount (ng/ng) peradsorbing film amount. From the results, it can be seen that a compositefilm with PAH increased the adsorbability as compared with the singlefilm of the bamboo vinegar solution.

EXAMPLE 3

[0092] In Example 3, removal tests of ethylene generated from apple isshown.

[0093] Two acrylic resin cases of cubes of 200 mm in each side wereprovided and apples were placed therein. In one of them, 50 g of abiodegradable resin foam to which 30 cc of the bamboo vinegar solutionobtained in Example 1 was attached and dried was arranged around theapples. On the other hand, in the other case, nothing was arrangedtherein. On the upper part of the cases were equipped fans respectivelyfor circulating the air in these systems.

[0094]FIG. 6 shows the results of ethylene gas concentration measuredafter 192-hour from the start of the experiment by use of a gasdetecting tube. The ethylene gas concentration in the case increased upto 100 ppm in the absence of the bamboo vinegar solution, due togeneration of ethylene from the apples. On the other hand, in thepresence of the bamboo vinegar solution, the ethylene gas concentrationin the case was suppressed to 5 ppm. Thus, a difference in concentrationwas 20 times.

EXAMPLE 4

[0095] The experiment was carried out in the same manner as in Example 3except that an extract solution obtained by extracting raw bamboo withan alcohol was used as a bamboo vinegar solution. As the bamboo vinegarsolution, a liquid obtained by charging 100 g of powdered raw green mosobamboo in a vessel and extracting with 70 cc of ethanol was used.

[0096]FIG. 7 shows the results. In the case where the bamboo vinegarsolution obtained from raw bamboo by extraction was used, the ethyleneconcentration in the case first increased up to 14 ppm but after about30 hours, it was continually suppressed to about 10 ppm.

EXAMPLE 5

[0097] Ethylene gas adsorbability was examined by using an extractsolution obtained by extracting raw bamboo with an alcohol as a bamboovinegar solution and varying the substrate. Three kinds of substrate,i.e., a biodegradable foamed material, silica gel and activated carbonwere used.

[0098] 15 g of each substrate was immersed in 100 ml of an aqueoussolution containing 1% chitosan for 10 minutes to treat the surface ofthe substrate. After annealing at 90° C. for 2 hours, the substrate wasimmersed in 100 ml of the bamboo extract solution for 10 minutes andsufficiently dried spontaneously. 15 g of the adsorbent thus producedwas charged in a 9-liter sealed vessel filled with 100 ppm of ethylenegas and ethylene gas was caused to be adsorbed while circulating the airby a fan. After 5 days, the removal rate of ethylene gas and theconcentration of ethylene glycol produced were measured. FIG. 8 showsthe results.

[0099] Since the specific surface area of the substrate increases inorder of biodegradable foamed material, silica gel and activated carbon,it can be seen from FIG. 8 that the removal rate of ethylene with thebamboo vinegar solution can be increased by increasing the specificsurface are of the substrate.

EXAMPLE 6

[0100] An example in which the adsorbent of the present invention wasused as a wrapping material of flowers is shown as follows.

[0101] As a wrapping material, cellophane paper coated with PAH to 2g/m² and further coated with the bamboo vinegar solution obtained inExample 1 to 5 g/m2 was used.

[0102] Six carnations in a bud stage were wrapped with the wrappingmaterial and charged in a 30-liter acrylic resin case, which was thensealed and stored at 25° C. for 3 days. During this period, the buds ofcarnation did not open at all and the size of the buds showed no change.However, when the carnations were taken out of the acrylic resin case,the buds were opened within 12 hours. This indicates that the wrappingmaterial of the present invention can suppress the maturation of theflowers.

EXAMPLE 7

[0103] Shown is an example in which the adsorbent of the presentinvention was used as a packaging material.

[0104] The packaging material was obtained by coating a tray made ofwood pulp and natural cellulose with a solution of chitosan in citricacid and further coating thereon with the bamboo vinegar solution (thesame solution as in Example 1).

[0105] On this tray were mounted apples and these were placed in asealed vessel and stored for 2 weeks while measuring the ethylene gasconcentration in the vessel for every 24 hours.

[0106] The ethylene gas concentration in the vessel was suppressed to 5ppm and the similar results as those in FIG. 6 were obtained.

EXAMPLE 8

[0107] Shown is an example in which the filter of the present inventionwas used for storage of perishables.

[0108] The filter of Example 1 was placed in an acrylic resin madesealed case of 200 mm in each side similar to that used in Example 1 andapples were arranged therein. The case was allowed to stand for 6 hoursand the measured concentration of the generated ethylene gas was 100ppm. The air in the sealed case was circulated by a fan through thefilter, the ethylene gas concentration in the case was then decreased to5 ppm. When the power of the fan was turned OFF and the case was allowedto stand for 6 hours again, the ethylene gas concentration in the sealedcase increased to 100 ppm again. But when the fan was turned ON tocirculate the air, the ethylene gas concentration was decreased to 5 ppmagain. FIG. 9 shows a change of ethylene gas concentration in the sealedvessel.

[0109] In the case where the maturation of apples is intended toaccelerate by use of the ethylene gas filter, the fan is kept OFF toincrease the ethylene gas concentration, while in the case where thematuration of apples is intended to delay, the fan is turned ON tomaintain the ethylene gas concentration at a low concentration.

EXAMPLE 9

[0110] Six roses in a bud stage were provided. Three of them werearranged in a usual room kept at 23° C. The remaining three were placedin a 1-m cubic vessel together with the filter holding the bamboovinegar solution on a biodegradable resin foam. For roses kept in ausual room, two among three withered after 5 days, while they were stillin the state of buds. On the other hand, for those kept in the vessel inwhich the bamboo vinegar solution was released, all the three witheredafter they completely bloomed.

EXAMPLE 10

[0111] In Example 10, a system for controlling the ethylene gasconcentration in the storage chamber of perishables by the feedbackcontrol type is shown.

[0112]FIG. 10 shows a schematic diagram of the concentration controlapparatus for a storage chamber. In FIG. 10, reference numeral 1 is astorage chamber for storing perishables such as fruits, 2 is perishablessuch as fruits to be stored, 3 is an ethylene gas bomb, 4 is an ethylenegas filter, 5 is a fan, 6 is an ethylene gas sensor, 7 is a measuringdevice, 8 is a personal computer, 9 is a feedback controller, and 10 isa solenoid valve.

[0113] Apples stored in the storage chamber 1 were kept in a lowconcentration ethylene gas atmosphere with turning the power of the fan5 ON and having ethylene gas that was released from the apples adsorbedon the filter during the time when no order for purchase was received.When it was approached three days before the delivery date according tothe purchase order received, the ethylene gas bomb was opened tointroduce ethylene gas into the storage chamber so that the apples couldbe ripened with ease. During this time, the filter was rotated at a lowspeed so as to the ethylene gas concentration in the storage chamberbecame 30 ppm. Immediately before shipment, the ethylene gasconcentration in the storage chamber was increased to 70 ppm and theapples were exposed to 70 ppm ethylene gas for 2 hours so as to theycould be shipped after they were completely ripened.

[0114]FIG. 11 shows a change of ethylene gas concentration in thestorage chamber by the ethylene gas concentration control system.

EXAMPLE 11

[0115] Next, application to a method and apparatus for measuring anethylene gas concentration will be shown.

[0116] The sensor obtained in Example 2 with the composite film of PAHand the bamboo vinegar solution was placed in a sealed vessel filledwith ethylene gas having a concentration of 8, 25, 30, 40, 200 or 600ppm and its response was observed. The same ethylene gas measuringapparatus shown in FIG. 3 as in Example 1 was used. The ethylene gasconcentration in the sealed vessel was measured by use of a commerciallyavailable detecting tube (manufactured by Gastec Corporation).

[0117]FIG. 12 shows the obtained results of adsorption isothermal curve.In FIG. 12, the horizontal axis indicates the ethylene gas concentrationin the sealed vessel and the vertical axis indicates ethylene gasadsorption amount measured by the QCM method. From FIG. 12, it can beseen that the curve is a Langmuir adsorption isothermal. This haslinearity at an ethylene gas concentration of 40 ppm or less and can beused as a simple ethylene gas concentration measuring apparatus havingthe same accuracy as that of the commercially available detecting tube.IF the ethylene gas concentration above 40 ppm, the curve is nonlinearbut conversion using a calibration curve makes it possible to similarlyuse the apparatus in the measurement of concentrations.

EXAMPLE 12

[0118] Specificity of the ethylene gas sensor of the present inventionto ethylene gas will be shown.

[0119] By using the QCM apparatus similar to that used in Example 1, 3ppm of formaldehyde, 80 ppm of trichloromethane and 40 ppm of ethylenewere filled in the sealed vessel. FIG. 13 shows the results. Thehorizontal axis indicates time and the vertical axis indicatesadsorption amount of ethylene. From FIG. 13, it can be seen that thesensor of the present invention adsorbed ethylene gas but did not adsorbother compounds such as formaldehyde and trichloromethane. From theresults, it can be seen that a sensor having adhered a bamboo vinegarsolution in the form of a film onto a quartz crystal microbalance has aselectivity to ethylene gas.

INDUSTRIAL APPLICABILITY

[0120] Ethylene gas adsorbent, wrapping material and packaging materialcontaining ethylene monooxygenase, in particular an alcohol extract ofraw bamboo can efficiently adsorb ethylene gas, so that they cansuppress maturation by ethylene gas generated form plants such asfruits, vegetables and flowers.

[0121] Further, ethylene gas concentration can be safely controlled tothe human body by use of a filter having supported thereon ethylenemonooxygenase. Such a controlling method can be applied to maintainingfreshness or controlling maturation of perishables such as fruits,vegetables and flowers in storage chamber or the like.

[0122] Furthermore, a quartz crystal microbalance having held thereonethylene monooxygenase or a bamboo vinegar solution can selectively andefficiently adsorb ethylene gas so that it can be applied to a methodand apparatus for measuring ethylene gas concentration.

1. An ethylene gas adsorbent comprising an alcohol extract solution ofraw bamboo.
 2. An ethylene gas adsorbent according to claim 1, whereinthe ethylene gas adsorbent is held on a substrate.
 3. An ethylene gasadsorbent according to claim 2, wherein the substrate is a transparentsheet-form material.
 4. An ethylene gas adsorbent according to claim 3,wherein the ethylene gas adsorbent is held on the substrate through agel forming substance having an amino group.
 5. A wrapping material orpackaging material for plants, comprising the ethylene gas adsorbentaccording to claim
 1. 6. A method for controlling a concentration ofethylene gas with a filter having held thereon an alcohol extractsolution of raw bamboo.
 7. A method for controlling a concentration ofethylene gas, comprising measuring an ethylene gas concentration of anatmosphere by an ethylene gas concentration measuring apparatus; anddecreasing the ethylene gas concentration by operating a fan to have theethylene gas adsorbed onto the filter according to claim 6 when theethylene gas concentration is equal to or above a predetermined value orintroducing ethylene gas into the atmosphere when the ethylene gasconcentration is equal to or below a predetermined value.
 8. A methodfor maintaining freshness or controlling maturation of perishables suchas fruits, vegetables, and flowers, comprising using the method forcontrolling ethylene gas concentration according to claim
 7. 9. Anapparatus for controlling ethylene gas concentration, comprising thefilter according to claim 6 and a fan.
 10. An apparatus for maintainingfreshness or controlling maturation of perishables such as fruits,vegetables, and flowers, comprising an ethylene gas concentrationmeasuring apparatus, the filter according to claim 6, and a fan.
 11. Anethylene gas sensor for sensing ethylene in a gas, characterized bycomprising a quartz crystal microbalance having coated thereon analcohol extract solution of raw bamboo.
 12. An ethylene gas sensoraccording to claim 11, wherein the quartz crystal microbalance is coatedwith the alcohol extract solution of raw bamboo through a gel formingsubstance having an amino group.
 13. A method for measuring aconcentration of ethylene gas in a gas by use of the ethylene gas sensoraccording to claim
 12. 14. A method for measuring a concentration ofethylene gas according to claim 13, wherein the concentration ofethylene gas is quantitatively determined by measuring a change in aneigen frequency of the quartz crystal microbalance.
 15. An apparatus formeasuring the concentration of ethylene gas, characterized by includingan ethylene gas sensor having an alcohol extract solution of raw bamboocoated on a quartz crystal microbalance; a device for measuring an eigenfrequency of the quartz crystal microbalance; a device for measuring achange in the eigen frequency; and a device for converting a value ofsaid change into an ethylene gas concentration.